Prevent crash when using getExtension while a PBO is bound.

gpu/command_buffer/service/feature_info.cc

Index: gpu/command_buffer/service/feature_info.cc
diff --git a/gpu/command_buffer/service/feature_info.cc b/gpu/command_buffer/service/feature_info.cc
index 6e81ab67bb16f6c40c3775b676c2420785689b79..b25aa088a05aba7d95c5e6fd8e074d793400d1d3 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -80,6 +80,30 @@ class StringSet {
   std::set<std::string> string_set_;
 };
 
+class ScopedPixelUnpackBufferOverride {
+ public:
+  explicit ScopedPixelUnpackBufferOverride(
+      ContextType context_type,
+      GLuint binding_override)
+      : original_binding_(0) {
+    if (!(context_type == CONTEXT_TYPE_WEBGL1 ||
+          context_type == CONTEXT_TYPE_OPENGLES2)) {
+      glGetIntegerv(GL_PIXEL_UNPACK_BUFFER_BINDING, &original_binding_);
+      glBindBuffer(GL_PIXEL_UNPACK_BUFFER, binding_override);

[Zhenyao Mo, 2016/08/29 19:18:48]

A minor optimization: if original_bindings_ == binding_override, then no
BindBuffer() calls.

This should also simplify the test expectations change.

[Ken Russell (switch to Gerrit), 2016/08/29 19:36:17]

Good point Mo. See also below.

[Kai Ninomiya, 2016/08/30 23:51:02]

Done.

+    }
+  }
+
+  ~ScopedPixelUnpackBufferOverride() {
+    if (original_binding_) {

[Ken Russell (switch to Gerrit), 2016/08/29 19:36:17]

Similar test could be done here to avoid restoring the binding if it was
unchanged.

[Kai Ninomiya, 2016/08/30 23:51:02]

Done.

+      glBindBuffer(GL_PIXEL_UNPACK_BUFFER,
+                   static_cast<GLuint>(original_binding_));
+    }
+  }
+
+ private:
+    GLint original_binding_;
+};
+
 }  // anonymous namespace.
 
 FeatureInfo::FeatureFlags::FeatureFlags()
@@ -752,6 +776,8 @@ void FeatureInfo::InitializeFeatures() {
     }
   }
 
+  ScopedPixelUnpackBufferOverride scoped_pbo_override(context_type_, 0);

[Ken Russell (switch to Gerrit), 2016/08/29 19:36:17]

I think you should move this up to the top of this method,
FeatureInfo::InitializeFeatures. Otherwise, the same bug is likely to crop up
again if someone inserts any extension checking code which calls TexImage2D.

[Kai Ninomiya, 2016/08/30 23:51:02]

Done.

+
   if (may_enable_chromium_color_buffer_float) {
     static_assert(GL_RGBA32F_ARB == GL_RGBA32F &&
                   GL_RGBA32F_EXT == GL_RGBA32F &&